1. (Field of the Invention)
This invention relates to starters, and more particularly to an overhang type starter with a dust protective device adapted to start a vehicle engine.
2. (Prior Art)
In a conventional starter of this type, a movable pinion cylinder is designed as disclosed, for instance, by Japanese Utility Model Application (OPI) No. 6679/1986 (the term "OPI" as used herein means an "unexamined published application").
FIG. 1 shows a conventional starter 1, in which reference numeral 2 designates a front frame; 3, a rotary output shaft; and 4, an overrunning clutch whose clutch outer 4a is spline-engaged with the rotary output shaft 3 in such a manner that it is slidable on the rotary output shaft 3. Further, in FIG. 1, reference character 4b designates friction rollers; 5, a movable pinion cylinder mounted on the rotary output shaft 3, the movable pinion cylinder 5 having the rear end portion formed into a clutch inner 4c; 6, a ball bearing which supports the middle portion of the movable pinion cylinder 5 on the front frame 2; 7 and 8, sleeve bearings; 9, a stopper mounted on the front end portion of the rotary output shaft 3; 10, a pinion formed on the front end portion of the movable pinion cylinder 5; 11, an engine ring gear; and 12, a bottommed cylindrical cap connected to the front end of the movable pinion cylinder 5 so as to close the front end opening 5a. The cap is long enough to cover the front end portion of the rotary output shaft 3. The cap 12 has an annular protrusion 12a forming the edge of its opening, which is engaged with an annular groove 5b formed in the movable pinion cylinder 5; that is, the cap 12 is detachably connected to the front end of the movable pinion cylinder 5.
The cap 12 is provided to prevent the entrance of dust through the front end opening 5a of the movable pinion cylinder 5, and it is made of resin such as "Nylon".
However, the conventional starter described above suffers from the following difficulties:
Since the cap 12 is completely closed, when the movable pinion cylinder 5 is moved forwardly by the shift lever 13, the space in the cap 12 is increased. When the movable pinion cylinder 5 is returned to its original position as shown in FIG. 1, the front end portion of the rotary output shaft 3 is allowed to go in the cap 12, so that the space in the cap 12 is decreased. As the space in the cap 12 changes as described above, the air pressure in the cap is changed. That is, in moving the movable pinion cylinder 5 forwardly, the negative pressure formed in the cap 12 will obstruct the movement of the movable pinion cylinder 5; and in returning the movable pinion cylinder, the air pressure in the cap 12 is increased, so that the cap may be caused to come off or may be damaged.